Nov 14, 2012 9:00am PST
rockies were sculpted by repeated glaciation. yosemite valley, here in the sierra nevada mountains, would have been another nondescript river valley if glaciers hadn't carved it to its present shape. many of the world's most beautiful lakes were gouged out of hard rock by glaciers, including north america's great lakes and the famous lochs of scotland. even the great expanses of rich agricultural soils that blanket china and the soviet union, canada and the united states owe their existence to glaciers. moving glacial ice pulverizes the underlying rock into silt-sized fragments. this silt was eventually transported and concentrated by the wind into the vast fertile soils of today. early scientists didn't really appreciate the important geological role of glaciers. even geologists were convinced that glaciers had never existed outside of their present locations over the last one million years. a breakthrough came in 1836 when swiss scientist louis agassiz reported evidence that the inhabitants of medieval villages in europe had moved their towns to keep pace with advancing glaciers.